"Disturbingly, since Iran’s multiple and ongoing violations of its NPT obligations have come to light, its leaders have hinted that they too are considering withdrawal" as North Korea did from the treaty in 2003, US special representative Christopher Ford told a conference of 130 nations on improving the global pact.
Ford said "withdrawal from the treaty cannot be seen as excusing prior violations or ending international efforts to take any appropriate measures to address violations committed prior to withdrawal."
He said UN-given equipment could be taken back from a state pulling out of the NPT and the state could automatically be referred to the UN Security Council, which could impose sanctions.
The conference in Vienna on the 189-nation NPT is considering ways to fix the landmark treaty, which came into effect in 1970 and which many complain has a flaw since it allows states to peacefully develop technology that can also be used to make atom bombs.
North Korea developed nuclear weapons after withdrawing from the NPT.
The United States charges that Iran is secretly developing the atomic bomb.
Although Tehran says its nuclear program is a peaceful effort to generate electricity, it is under UN sanctions for defying a Security Council call for it to stop enriching uranium, which can be used as raw material for the bomb.
The UN watchdog International Atomic Energy Agency had in February 2006 found Iran in violation of the NPT for hiding sensitive nuclear work.
A Western diplomat told AFP the United States had brought up the withdrawal issue Wednesday to make sure Iran could not block this being part of the official record when the conference’s conclusions are drawn on its closing day Friday.
The two-week meeting which opened April 30 has already been crippled by procedural wrangling. It is the first of a series of conferences to prepare for an overall review of the NPT in 2010.
Iran accepted an agenda compromise Tuesday that saved the meeting from collapse after six working days of deadlock.
Several Western diplomats had charged that Iran was blocking the meeting in order to avoid further condemnation over its defiance of UN sanctions.
French ambassador Jean-Francois Dobelle on Wednesday said "it may be considered that Iran is failing to comply with any of the conditions laid down in Article IV (of the NPT) for entitlement to exercise its right to nuclear energy."
Other speakers stressed the obligations of nuclear weapons states to give security guarantees to nations that forego developing atomic weapons.
"What is also required is for such states not to feel threatened by nuclear weapons," said South African ambassador Abdul Samad Minty.
"The granting of legally binding security assurances" would fulfill "the undertaking which should be given to the states that have voluntarily given up the nuclear-weapons option by becoming parties to the treaty," Minty said.
South Korean ambassador Dong-hee Chang said that since there was disagreement on such guarantees, called negative security assurances, states should strive to set up regional nuclear weapons free zones.
Indonesia, speaking for non-aligned states, said however that "non-nuclear-weapon states should be effectively assured by nuclear-weapon states that there will be no use or threat of nuclear weapons."